The invention relates to an apparatus for determining the status of a valve arrangement forming part of a fuelling system. In particular, the invention relates to an apparatus for monitoring the status of a pressure raising shut-off valve arrangement forming part of a fuelling system for an aircraft engine. The invention also relates to a method for determining the status of such a valve arrangement.
In a conventional fuelling system for an aircraft engine, a plump receives fuel at relatively low pressure through an inlet passage, the pump being driven by means of a drive shaft associated with the engine. The pump delivers fuel through a pump outlet to a metering valve arrangement and a pressure raising shut-off valve arrangement (PRSOV) which serve to regulate fuel flow to the engine. The metering valve and the pressure raising shut-off valve are responsive to signals from an electronic control circuit which, in turn, is responsive to signals from the engine and the metering valve arrangement. The provision of the pressure raising shut-off valve ensures fuel is only supplied to the engine when feel flow through the valve is of sufficiently high pressure.
Fuel flow to the engine can be modulated by moving the metering valve between a maximum flow and a minimum flow position. The pressure raising shut-off valve can be closed at any time, on demand, if it is required to shut-off the fuel supply to the engine. This may occur as a result of normal engine operation or as an emergency shut-off in the event of the occurrence of a fault, for example overspeed or fire.
For safety reasons, it is necessary to ascertain whether the pressure raising shut-off valve will close correctly upon shut-down of the engine. One step in the engine start-up procedure is therefore to check whether the pressure raising shut-off valve will close correctly during operation of the engine if normal or emergency shut-off is demanded. If a fault is detected, the subsequent engine start-up procedure is not initiated.
It is known to use microswitches to monitor the position of the shut-off valve so as to determine whether the valve will close correctly during the engine shut-down procedure and during the engine start-up procedures. When the pressure raising shut-off valve is moved to its closed position, the microswitches are closed to make an electrical connection, the absence of any resulting electrical signal indicating that closure of the shut-off valve did not occur correctly. The operation of the microswitches can, however, be unreliable. Another proposed solution is to use an inductive sensor in place of the microswitches. However, such solutions require additional wiring to be incorporated on the shut-off valve and within the electronic control unit. Furthermore, inductive sensors are relatively expensive components.
It is an object of the present invention to provide an apparatus and method for monitoring the position of a shut-off valve arrangement forming part of a fuelling system which alleviates or overcomes one or more of the aforementioned problems.
According to a first aspect of the present invention, an apparatus for determining the status of a shut-off valve arrangement forming part of a fuelling system of an engine comprises;
a metering valve arrangement comprising a metering valve member for regulating fuel flow from a pump to the engine and means for monitoring the position of the metering valve member,
the metering valve member being operable between a maximum flow position in which a maximum flow of fuel flows through the metering valve arrangement to the shut-off valve arrangement, and a minimum flow position in which a minimum flow of fuel flows through the metering valve arrangement to the shut-off valve arrangement,
means for varying fuel pressure acting on the metering valve member upon closure of the shut-off valve arrangement, and
means for monitoring the response of the metering valve arrangement to the variation in fuel pressure so as to provide an indication that the shut-off valve arrangement has closed.
The invention provides the advantage that the need for microswitches or an inductive sensor for measuring the position of a shut-off valve member forming part of the shut-off valve arrangement is removed.
Conveniently, the metering valve arrangement includes first and second control chambers associated with respective ends of the metering valve member, the position of the metering valve member being controlled by controlling fuel pressure within at least one of the first and second control chambers.
Fuel pressure within the first and second control chambers may be controlled by means of a servo-valve supplied with a current.
The current supplied to the servo-valve is conveniently controlled by means of an electronic engine controller, the current being supplied by any suitable current source.
The position sensing means conveniently takes the form of an LVDT. The LVDT enables the position of the metering valve member to be accurately measured.
In one embodiment of the invention, the apparatus comprises means for reducing fuel pressure acting on one end of the metering valve member upon closure of the shut-off valve arrangement. For examples the shut-off valve arrangement may be adapted to include a porting arrangement arranged such that, upon closure of the shut-off valve arrangement, fuel pressure within one of the first and second control chambers is caused to be reduced. In one embodiment, the shut-off valve arrangement may be provided with a port in communication with a low pressure reservoir, the port being brought into communication with one of the first or second control chambers associated with the metering valve member upon closure of the shut-off valve arrangement.
Upon closure of the shut-off valve arrangement, there is a reduction in fuel pressure acting on one end of the metering valve member which serves to urge the metering valve member towards the minimum flow position. The electronic metering valve position control loop senses the change in position of the metering valve member and increases the electrical current supplied to the servo-valve, thereby decreasing the pressure of fuel acting on the other end of the metering valve member to oppose the movement towards the minimum flow position.
The relative sizes of the additional port on the shut-off valve arrangement and a port on the servo-valve may be arranged such it either (i) the metering valve member continues to move towards the minimum flow position or (ii) the metering valve is prevented from moving towards the minimum flow position. In case (i), movement of the metering valve member is sensed by the position sensing means which generates an output signal which provides an indication that closure of the shut-off arrangement has occurred correctly. In case (ii), an increase in the current supplied to the servo-valve is detected within the electronic control loop and is used to provide an indication that closure of the shut-off valve arrangement has occurred correctly.
In an alternative embodiment of the invention, the apparatus comprises means for increasing fuel pressure acting on one end of the metering valve member upon closure of the shut-off valve arrangement. For example, the shut-off valve arrangement may be adapted to include a porting arrangement such that, upon its closure, fuel pressure acting on one end of the metering valve member is increased.
In one embodiment, the shut-off valve arrangement may be provided with a port in communication with a source of high pressure fuel, as opposed to a low pressure fuel reservoir, the port being brought into communication with one of the first or second control chambers associated with the metering valve member upon closure of the shut-off valve arrangement.
The invention may also provide the further advantage that existing fuelling systems can be adapted relatively easily by providing two additional ports on the shut-off valve arrangement without the need for additional wiring on the shut-off valve arrangement and within the electronic engine controller.
Alternatively, the shut-off valve arrangement may include a pressure control chamber, fuel pressure within the pressure control chamber being varied so as to control the position of the shut-off valve member, whereby an increase in fuel pressure within the pressure control chamber causes closure of the shut-off valve arrangement. Preferably, the shut-off valve arrangement is provided with a fiber port in communication with the first control chamber of the metering valve arrangement, the further port being arranged such that, upon closure of the shut-off valve arrangement, the finder port is brought into communication with the pressure control chamber, thereby causing fuel at relatively high pressure to be delivered to the fist control chamber so as to urge the metering valve member towards the minimum flow position.
When it is desired to close the shut-off valve arrangement, fuel pressure within the pressure control chamber thereof is increased. Upon movement of the shut-off valve member towards its closed position, the further port is brought into communication with the pressure control chamber and, hence, high pressure fuel within the pressure control chamber is delivered to the first control chamber of the metering valve arrangement, thereby serving to urge the metering valve member towards the minimum flow position.
This embodiment of the invention provides the further advantage that, during normal operation when the shut-off valve arrangement is open, leakage of fuel to low pressure through the shut-off valve a arrangement can be substantially avoided.
The metering valve arrangement may alternatively include a third control chamber arranged such that, upon closure of the shut-off valve arrangement, fuel pressure within the third control chamber is increased, a force due to increased fuel pressure within the third control chamber acting in combination with a force due to fuel pressure within the first control chamber to urge the metering valve member towards the minimum flow position.
In this embodiment of the invention, the pressure of fuel within the third control chamber is not controlled by the servo-valve. This embodiment of the invention therefore provides the advantage that any problems which may arise during normal metering of the fuel system due to the provision of an additional port on the shut-off valve arrangement in communication with a chamber of the metering valve member, the pressure within which is controlled by the servo-valve, is avoided, as the port on the shut-off valve arrangement communicates with the third control chamber.
The shut-off valve arrangement preferably includes a shut-off valve member provided with an annular chamber defined, at least in part, by a recess or groove provided on the shut-off valve member, whereby the annular chamber communicates with the third control chamber depending on the position of the shut-off valve member, thereby permitting fuel at high pressure to flow into the third control chamber so as to urge the metering valve member towards the minimize flow position upon closure of the shut-off valve arrangement.
The metering valve member may conveniently be provided with a restricted drilling which permits fuel to flow from the third control chamber to a low pressure fuel reservoir at a relatively low rate.
As described previously, in embodiments of the invention in which fuel pressure applied to the metering valve member is varied upon closure of the shut-off valve arrangement, the position of the metering valve member may be monitored by the position sensing means so as to monitor the response of the metering valve arrangement to the variation in fuel pressure applied thereto.
As the metering valve member is urged towards its minimum flow position, the electronic controller provides a signal which tends to increase the current supplied to the servo-valve so as cause the metering valve member to be maintained in a demanded metering position.
In any of the embodiments of the invention, the apparatus may be arranged such that the metering valve member does move to its minimum flow position upon closure of the shut-off valve arrangement. In this case, the current supplied to the servo-valve must therefore be limited such that it does not exceed a predetermined limit. The current may conveniently be limited by appropriate programming of the electronic engine controller.
The apparatus may therefore comprise means for determining whether an output signal generated by the position sensing means which is indicative of movement of file metering valve member to the minimum flow position is accompanied by a command signal to initiate movement of the metering valve member to the minimum flow position and, in the event that it is not, for generating a filer output signal to provide an indication that closure of the shut-off valve arrangement has occurred.
Alternatively, the apparatus may comprise means for determining whether an output signal generated by the position sensing means indicative of movement of the metering valve member into the minimum flow position is accompanied by a command signal to initiate closure of the shut-off valve arrangement and for generating a further output signal to provide an indication that closure of the shut-off valve arrangement has occurred correctly.
Alternatively, in any of the embodiments of the invention, the response of the metering valve arrangement to the variation in fuel pressure may be monitored by measuring the current supplied to the servo-valve to maintain the metering valve member in the demanded metering position. In this case, the current need not be limited.
The apparatus may therefore include means for measuring the current supplied to the servo-valve, whereby the current supplied to the servo-valve so as to maintain the metering valve member in the demanded metering position is measured to provide an indication of the status of the shut-off valve arrangement.
Means may be provided for generating a further output signal to provide an indication that closure of the shut-off valve arrangement has occurred in the event that the current measured by the current sensing means exceeds a predetermined amount, indicative of movement of the metering valve member towards the minimum flow position, and this is accompanied by a command signal to initiate closure of the shut-off valve arrangement.
Alternatively, the apparatus may comprise means for determining whether an output signal generated by the current measuring means which is indicative of movement of the metering valve member towards the minimum flow position is accompanied by a command signal to initiate movement of the metering valve member to the minimum flow position and, in the event that it is not, for generating a further output signal to provide an indication that closure of the shut-off valve arrangement has occurred.
According to a second aspect of the present invention, there is provided a method for determining the status of a shut-off valve arrangement forming part of a fuel system of an engine, the method comprising the steps of;
providing a metering valve arrangement for regulating fuel flow from a pump to the engine comprising a metering valve member and means for controlling the position of the metering valve member, the position of the metering valve member being controlled by controlling fuel pressure within a control chamber which acts on the metering valve member,
varying fuel pressure acting on the metering valve member upon closure of be shut-off valve arrangement so as to urge the metering valve member towards a minimum flow position, and
monitoring the response of the metering valve arrangement so as to provide an indication of the states of the shut-off valve arrangement.
Preferably, the method includes the step of increasing fuel pressure acting on the metering valve member to urge the metering valve member towards the minimum flow position.
Preferably, the method includes the step of controlling the position of the metering valve member by means of a servo-valve supplied with a current;
In one preferred embodiment, the method comprises the steps of;
limiting the current supplied to the servo-valve such that it cannot exceed a predetermined amount, thereby causing the metering valve member to move into the minimum flow position upon closure of the shut-off valve arrangement;
sensing the position of the metering valve member using position sensing means and generating an output signal indicative of the position of the metering valve member, and
using the output signal from the position sensing means to provide an indication that closure of the shut-off valve arrangement has occurred.
The predetermined amount is less than the minimum current required to maintain the metering valve member in a maximum flow position when the shut-off valve arrangement has closed, the current supplied to the servo-valve causing the pressure applied to the metering valve control chamber to oppose the force due to fuel at high pressure urging the metering valve member towards the minimum flow position.
Alternatively, in another preferred embodiment of the invention, the method may include the steps of;
measuring the current supplied to the servo-valve and
using the measured current to provide an indication of the status of the shut-off valve arrangement.
Preferably, the method may comprise the step of determining that the shut-off valve arrangement has closed when the measured current exceeds a predetermined amount.